Nanosized poly(methyl methacrylate) (PMMA) particles with a high molecular weight of 10(6) g mol(-1) and a polydispersity index of about 1-2 were synthesized, for which 2,2'-azobisisobutyronitrile was used as the initiator and a differential microemulsion polymerization technique was employed. The kinetics of the polymerization, the glass transition temperature, tacticity, the particle size distribution, and the morphology of the nanosized PMMA synthesized were investigated. The dependence of the number of the polymer particles (N-p) and the number of the micelles (N-m) on the concentration of the surfactant was discussed. The molecular weight distribution was found to be nearly constant over the polymerization time, which was attributed to the significance of micellar polymerization. The resultant nanosized PMMA has a rich syndiotactic configuration (53-57% rr triads) with a glass transition temperature of about 125 degrees C. A beneficial operation condition was discovered where the conversion reached a maximum at a high monomer-to-water ratio. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 375-382, 2009